The Ministry Of God's Two Witnesses
The powerful, miracle-filled ministry of God's end-time two witnesses (who will be two modern-day human beings, just as every single one of God's Prophets have been throughout Bible History e.g. Elijah was a human prophet of his own time, John The Baptist was a human prophet of his own time - see The Elijahs) will last 1,260 days, which is 3½ years. The return of Jesus Christ will happen shortly after those two prophets are martyred (angels can't be killed, so those who claim that the two witnesses will be angels have an unworkable theory, just as those who have come up with the idea that the two witnesses are somehow the Old and New Testaments) and resurrected in Jerusalem.
"And when they have finished their testimony, the beast that ascends from the bottomless pit will make war upon them and conquer them and kill them, and their dead bodies will lie in the street of the great city which is allegorically called Sodom and Egypt, where their Lord was crucified. For three days and a half men from the peoples and tribes and tongues and nations gaze at their dead bodies and refuse to let them be placed in a tomb, and those who dwell on the earth will rejoice over them and make merry and exchange presents, because these two prophets had been a torment to those who dwell on the earth."
"But after the three and a half days a breath of life from God entered them, and they stood up on their feet, and great fear fell on those who saw them. Then they heard a loud voice from heaven saying to them, "Come up hither!" And in the sight of their foes they went up to heaven in a cloud."
"And at that hour there was a great earthquake, and a tenth of the city fell; seven thousand people were killed in the earthquake, and the rest were terrified and gave glory to the God of heaven."
"The second woe has passed; behold, the third woe is soon to come."
"Then the seventh angel blew his trumpet, and there were loud voices in heaven, saying, "The kingdom of the world has become the kingdom of our Lord and of his Christ, and He shall reign for ever and ever." And the twenty-four elders who sit on their thrones before God fell on their faces and worshiped God, saying, "We give thanks to thee, Lord God Almighty, Who art and who wast, that Thou hast taken Thy great power and begun to reign." (Revelation 11:3-17 RSV)
Fact Finder: How did Jesus Christ describe world conditions in the time prior to His return?